Methods of manufacturing a MEMS device having a backplate with elongated protrusions

ABSTRACT

MEMS devices with a rigid backplate and a method of making a MEMS device with a rigid backplate are disclosed. In one embodiment, a device includes a substrate and a backplate supported by the substrate. The backplate includes elongated protrusions.

This application is a divisional application of application Ser. No.13/750,941 filed on Jan. 25, 2013, which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates generally to a system and a method formanufacturing a micro-electromechanical system (MEMS) package, and, inparticular embodiments, to a system and a method for manufacturing aMEMS microphone package.

BACKGROUND

Over the past years a desire for smaller electronic form factors andpower consumption along with increased performance has driven anintegration of device components. One area where integration took placeis area of MEMS devices. More specifically, microphones in electronicdevices such as, e.g., cell phones, laptops, and tablets arepredominately MEMS microphones.

A MEMS (Micro-Electrical-Mechanical System) microphone comprises apressure-sensitive diaphragm disposed in a silicon chip. The MEMSmicrophone is sometimes integrated with a preamplifier into a singlechip. MEMS microphones may also include an analog-to-digital converter(ADC) circuit making it a digital MEMS microphone.

SUMMARY OF THE INVENTION

In accordance with an embodiment a device comprises a substrate and abackplate supported by the substrate, wherein the backplate compriseselongated protrusions.

In accordance with another embodiment a MEMS structure comprises amovable electrode supported by a substrate and a counter electrodesupported by the substrate, wherein the counter electrode compriseselongated protrusions.

In accordance with yet another embodiment a method for manufacturing aMEMS structure comprises forming a sacrificial layer over a substrateand forming recesses in the sacrificial layer, the recesses comprising afirst type of recess and a second type of recess, the first type ofrecess being different than the second type of recess. The methodfurther comprises filling the first and second types of recesses with aconductive material, removing a portion of the substrate underneath theconductive material and removing the sacrificial layer.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1 a and 1 b show a microphone device that can include embodimentsof the present invention;

FIG. 2 a shows a top view of an embodiment of backplate of a MEMSstructure comprising elongated protrusions;

FIGS. 2 b and 2 c show cross sectional views of an embodiment of abackplate and a membrane comprising elongated protrusions;

FIGS. 3 a-3 c show top views of an embodiment of a backplate withelongated protrusions;

FIGS. 4 a-4 c show top views of an embodiment of a backplate withelongated protrusions;

FIGS. 5 a and 5 b show top views of an embodiment of a backplate withelongated protrusions;

FIGS. 6 a-6 d show top views of an embodiment of a backplate withelongated protrusions; and

FIG. 7 shows a flow chart of an embodiment of a method for manufacturinga MEMS structure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to embodiments in aspecific context, namely sensors or microphones. The invention may alsobe applied, however, to other MEMS structures or transducers such aspressure sensors, RF MEMS, accelerometers and actuators.

FIG. 1 a shows a cross sectional view of a microphone device 100. Themembrane 130 and the backplate 150 form a static or parasiticcapacitance along the support structure 140 (shown with a capacitor signin FIG. 1 a). To decrease the static capacitance, the membrane 130 andthe backplate 150 may only partially overlap as shown in FIG. 1 b. Thebackplate 150 of the microphone device 100 is typically rigid. Inconventional devices, the rigidity of the backplate 150 can be increasedby increasing the thickness of the backplate 150 and thereforeincreasing the bending stiffness. However, a problem with increasing thestiffness of the backplate 150 is that a thicker backplate increases theresistance of the perforation holes since they are thicker now andtherefore the noise of the microphone device 100.

Alternatively, the rigidity of the backplate 150 can be increased byincreasing the tensile stress of a stress layer in the backplate 150.However, a problem with increasing the tensile stress is that itinfluences the membrane spring constant. Moreover, in both cases stressis concentrated in the anchor region where the backplate is connected tothe substrate 110. The anchor region is typically the area where afracture starts in case of extreme overload pressure.

Embodiments of the invention increase the rigidity of the backplate 150by, for example, including elongated protrusions. As such, a MEMSstructure with a stiff backplate and a long reliable lifetime can beachieved. These embodiments can be used in conjunction with thetechniques described above.

An embodiment of the invention provides elongated protrusions in thebackplate, for example of the MEMS device shown in FIGS. 1 a and 1 b. Invarious embodiments the elongated protrusions are disposed in, at oraround the anchor regions. The elongated protrusions may be placed atthe areas with maximum stress concentration. The elongated protrusionsmay be disposed on the backplate facing towards the membrane or facingaway from the membrane.

An advantage is that the elongated protrusions are fabricated in thesame process as the anti-sticking bumps. A further advantage is that aselective increase in backplate thickness increases the bendingstiffness of the backplate by a power of three (e.g., two times thebackplate thickness adds eight times bending stiffness). Therefore, thethickness of the backplate does not need to be increased over the entirebackplate surface but only at strategic important locations such as theanchor regions.

FIG. 2 a shows a top view of an embodiment of a MEMS structure 200. TheMEMS structure 200 comprises a substrate 210, a membrane 220 and abackplate 230. The substrate 210 comprises a rim 215 and the backplate230 is anchored or bridged to the rim 215 of the substrate 210 in anchorregions 240. An opening (or back-volume or sound port) is disposed inthe substrate 210 beneath the membrane 220 and the backplate 230 (notshown).

The membrane 220 and the backplate 230 are mechanically connected to asubstrate 210 along their circumference. The membrane 220 and thebackplate 230 may be circular or square. Alternatively, the membrane 230and the backplate 260 may comprise any geometrical suitable form.

The substrate 210 may include a bulk mono-crystalline silicon substrate(or a layer grown thereon or otherwise formed therein), a {110} silicon,a {100} silicon, a silicon-on-insulator (SOI), or agermanium-on-insulator (GeOI). In various embodiments, the substrate 210may include blanket epitaxial layers. The substrate 210 may comprise acompound semiconductor substrate such as indium antimonide, indiumarsenide, indium phosphide, gallium nitride, gallium arsenide, galliumantimonide, lead telluride, silicon germanium, silicon carbide orcombinations thereof or glass.

The movable electrode or membrane 220 may comprise a conductive materialsuch as polysilicon, doped polysilicon, a metal, or combinationsthereof. Alternatively, the membrane 220 may comprise at least one ormore additional dielectric layers.

The backplate or counter electrode 230 may comprise a conductivematerial such as polysilicon, doped polysilicon, a metal, orcombinations thereof. Alternatively, the backplate 230 may comprise oneor more additional layers. The additional layers may comprise adielectric layer such as a silicon nitride layer, a silicon oxynitridelayer, an oxide layer or a polymeric layer. The dielectric layer may beconfigured to provide tensile stress. The backplate 230 is perforated232 to reduce damping effects. The membrane 220 may be disposed below orabove the backplate 230.

The backplate 230 comprises anti-sticking bumps 234. The anti-stickingbumps 234 may be circular, rectangular or square regions with protrudingportions. The protruding portion may be a middle tip or middle point.

The backplate 230 further comprises elongated protrusions such asstiffening ridges, stiffening lines, stiffening routes, stiffeningtracks and/or corrugation lines 236. The elongated protrusions 236 arelonger and/or wider than the anti-sticking bumps 234. The elongatedprotrusions 236 are disposed on the anchor fingers, anchor bridges,attachment regions, anchor bars or anchor spokes 238 of the backplate230. Alternatively, the elongated protrusions are only or are alsodisposed in the central region 239 of the backplate 230. The anchorfingers, anchor bridges or attachment regions 238 may comprise 10% to40% of a radius of the backplate 230 and the central region 239 maycomprise 60% to 90%. In one particular embodiment, the anchor fingers238 comprise 30% of the radius of the backplate 230 and the centralregion 239 comprises 70% of the radius.

The anchor fingers 238 may be equally spaced from each other and maycomprise the same width wA and the same length 1A. Alternatively, theanchor fingers 238 may comprise different widths wA and differentlengths 1A, and may be spaced in different distances from each other.

In one embodiment the elongated protrusions 236 are disposed on thebackplate 230 in a radial direction. The elongated protrusions 236 maybe disposed on the backplate 230 close to a circumference of thebackplate 230 and may overlie a rim region 215 and the anchor bridge238. In one embodiment the elongate protrusions 236 overlie and gothrough a center point of the backplate 230.

FIG. 2 a shows a single elongated protrusion 236 per anchor bridge 238.The elongated protrusions 236 may comprise half the width of the anchorbridge 238. Alternatively, the elongated protrusions 236 may compriseother width dimensions. The elongated protrusions 236 may be connectedto each other through peripheral regions of the central region 239.

FIG. 2 b shows an embodiment of a cross sectional view of a portion of abackplate 230 and the membrane 220. The backplate 230 comprises ananti-sticking bump 234 and an elongated protrusion 236 (e.g., stiffeningridges, stiffening lines, stiffening routes or stiffening tracks). Thebackplate 230 comprises a dielectric layer 231. The dielectric layer 231may comprise a dielectric material such as silicon nitride, siliconoxynitride, silicon oxide or a polymeric. The dielectric layer 231 maybe tensile stressed. The backplate 230 is perforated to reduce dampingeffects (not shown).

The backplate 230 further comprises a conductive layer 233. Theconductive layer 233 may comprise a polysilicon layer that is doped orundoped. The conductive layer 233 may comprise another doped or undopedsemiconductive layer.

In some embodiments, the conductive layer 233 may comprise a metalliclayer. The metallic layer may comprise a metallic material, such as apure metal, an alloy and/or a compound. It is understood that any puremetal may include trace impurities. The metallic material may includeone or more of the Periodic Table elements selected from the groupconsisting of Al (aluminum), Cu (copper), and Au (gold). Examples ofpossible metallic material which may be used include, withoutlimitation, pure aluminum, aluminum alloy, aluminum compound, purecopper, copper alloy, copper compound, pure gold, gold alloy and goldcompound.

Alternatively, the conductive layer 233 may comprise an otherwiseconductive material.

The conductive layer 233 may be disposed on the dielectric layer 231.Alternatively, the dielectric layer 231 may be disposed on theconductive layer 233.

In one embodiment the backplate 230 comprises a sandwich structure,e.g., a stack of a dielectric layer 231, a conductive layer 233, and adielectric layer 231 or a stack of a conductive layer 233, a dielectriclayer 231 and a conductive layer 233. Alternatively, the backplate 230comprises a stack comprising a plurality of conductive layers 233 and aplurality of dielectric layers 231.

In certain embodiments, the conductive layer 233 of the backplate has athickness dC of about 1000 nm to about 2000 nm and a dielectric layer231 having a thickness dD of about 100 nm to about 200 nm. The thicknessdC of the conductive layer 233 is about 10 times larger than thethickness dD of the dielectric layer 231. In a particular embodiment,the thickness dC of the conductive layer 233 is about 1500 nm and thethickness dD of the dielectric layer 231 is about 140 nm. The topsurface 230 a of the backplate 230 is substantially planar for theanti-sticking bump 234 and the elongated protrusion 236. For example,the elongated protrusion 236 may comprise a T shape. The width wR of theelongated protrusion 236 may be chosen such that the top surface 230 aof the backplate 230 is substantially planar.

The width wR of the elongated protrusion 236 may be chosen so that thewidth wR is less than or equal to twice the thickness of the backplate230. The thickness of the backplate 230 may be the combined thickness ofthe conductive layer 233 (e.g. thickness dC) and dielectric layer 231(e.g. thickness dD). The elongated protrusion 236 may be a ridge such asa stiffening ridge.

The height hR of the elongated protrusion 236 may be the same as thecombined thickness of the conductive layer 233 and the dielectric layer231 dC and dD. The height hR may be about 0.5 μm to about 1.5 μm anddepends on the preform structure defined in the underlying sacrificiallayer. The elongated protrusion 236 and the anti-sticking bump 234 aredisposed on the side of the backplate 230 which faces the membrane 220.

In one or more embodiments, the backside 231 a of the backplate 230, atthe elongated protrusion 236, may be substantially flat, e.g., as shownin FIG. 2 b. In one or more embodiments, there may be substantially norecess in the backside 231 a of the backplate 230 at the elongatedprotrusion 236.

In one or more embodiments, the backside 231 a of the backplate 230, atthe anti-sticking bump 234, may be substantially flat. In one or moreembodiments, there may be substantially no recess in the backside 231 aof the backplate 230 at the anti-sticking bump 234. In the embodimentshown, the elongated protrusion 236 may comprise a T shape.

FIG. 2 c shows a cross sectional view of a further embodiment of aportion of a backplate 230 and a membrane 220. FIG. 2 c shows abackplate 230 similar to that in FIG. 2 b but with an additionalelongated protrusion 235. The elongated protrusion 235 may be acorrugation line. In the embodiment shown, the elongated protrusion 235is wider than the elongated protrusion 236 and the anti-sticking bump234. In the embodiment shown, the elongated protrusion 235 comprise arecess RES in the backside surface 230 a of the backplate 230. Therecess RES in the backside of the surface 230 a comprise may comprise aU shape. Likewise, the elongated protrusion 235 may comprise a U shape.In one or more embodiments, the width wCo of the elongated protrusion235 may be larger than twice the thickness of the backplate (e.g., thecombined thickness of the conductive layer 233 and the dielectric layer231 dC and dD).

The elongated protrusions 235, 236 may provide for increased stiffeningof the backplate 230 in a direction along (e.g. parallel to) thedirection of the elongation. Hence, they may make the backplate 230stiffer in a direction parallel to the direction of the elongation. Inthe embodiment shown in FIG. 2 c, the direction of elongation for eachof elongated protrusion 235 and elongated protrusion 236 isperpendicular to the page. In one or more embodiments, the direction ofthe elongation may made to run in a direction which is radial on thebackplate 230. This is shown, for example, in FIG. 2 a which theelongated protrusion 236 on the anchor bridge 238 runs in a direction(that is, the elongation is in a direction) which is radial on thebackplate.

The elongated protrusion 235 may make the backplate 230 more flexible ina direction that is perpendicular to the direction of the elongation. Inone or more embodiments, the direction of elongation may run parallel tothe backplate's 230 circumference (e.g., which may comprises a circle, asquare or a star configuration). The elongated protrusion 236 may beconfigured to decouple the backplate 230 from the substrate and fromsubstrate/body noise/vibration.

FIG. 3 a shows a top view of an embodiment of a MEMS structure 300. Thebackplate 330 and the membrane (not shown) are mechanically connected toa substrate 310 along their circumference. The membrane and thebackplate 330 may comprise a circular like, a square like form or a starlike form. Alternatively, the membrane and the backplate 330 maycomprise any geometrical suitable form.

The membrane and the backplate 330 may be connected to the substrate 310via an anchor region. The substrate 310 may further include activecomponents such as transistors, diodes, capacitors, amplifiers, filtersor other electrical devices. The substrate 310 may include an integratedcircuit (IC). The MEMS structure 300 may be a stand-alone device or maybe integrated with an IC into a single chip.

The membrane and the backplate 330 comprise a conductive material. Theconductive material may comprise a polysilicon material such as a doped(or undoped) polysilicon. The conductive material may comprise ametallic material. The membrane and backplate may comprise a combinationof materials. The membrane and backplate may comprise a combination ofconductive layers with dielectric layers such as silicon nitride,silicon oxynitride, oxide (e.g. silicon oxide) or polymeric layers. Thedielectric layer may be a tensile stress layer. The backplate 330 may beperforated to reduce damping effects when in operation.

The backplate 330 comprises cutouts 320 along the circumference 336 ofthe backplate 330. The cutouts 320 form anchor bridges 340 connectingthe backplate 330 to the substrate 310. The cutouts 320 alternate withthe anchor bridges 340. The cutouts 320 may comprise a parabola or aparabola like form. Alternatively, the cutouts 320 may comprise an oval,an oval like, a circular or a circular like form.

FIG. 3 b shows a detailed view of the anchor bridges 340. Elongatedprotrusions 352 are disposed only on the anchor bridges 340. There arefour elongated protrusions 352 per anchor bridge 340. Alternatively,there are other numbers of elongated protrusions 352 per anchor bridge340. Moreover the elongated protrusions 352 comprise a length 1R withless than half of the length 1A of the anchor bridge 340. Alternativelythe length 1R of the elongated protrusions 352 may be as large as thelength 1A of the anchor bridges 340 or even longer. In otherembodiments, the elongated protrusions 352 overlie the rim region 315and the opening beneath the membrane and the backplate 330. Theelongated protrusions 352 may be stiffening ridges, stiffening lines,stiffening routs, stiffening tracks or corrugation lines.

FIG. 3 c shows elongated protrusions 352 disposed on the anchor bridges340 and a peripheral region 337 of a central region 335 of the backplate330. There are four elongated protrusions 352 per anchor bridge 340 andtwo elongated protrusions 353 connecting an anchor bridge 340 with thetwo neighboring anchor bridges 340. Alternatively, there are othernumbers of elongated protrusions 352, 353 per anchor bridge 340.Moreover, the elongated protrusions 352 comprise a length 1R having alength less than half of the length 1A of the anchor bridge 340.Alternatively the length 1R of the elongated protrusions 352 may be aslarge as the length 1A of the anchor bridges 340 or even longer. Inother embodiments, the elongated protrusions 352 overlie the rim region315 and the opening beneath the membrane and the backplate 330. Theelongated protrusions 352 are disposed along the circumference of thecutout 320 connecting neighboring anchor bridges 340.

The backplate 330 further comprises anti-sticking bumps 339 andanti-dampening openings 338. The anti-sticking bumps 339 may comprise acircular, a rectangular or a square region with a protruding portion.The protruding portion may be a middle tip or middle point. Theelongated protrusions 352 may be a stiffening ridge, a stiffening line,a stiffening route, a stiffening track or a corrugation line. Theelongated protrusion 352 and the anti-sticking bumps 339 may be planaron the backside. The anti-sticking bumps 239 are be elongatedprotrusions.

FIG. 4 a shows a top view of an embodiment of a MEMS structure 400. Thebackplate 430 and the membrane (not shown) are mechanically connected toa substrate 410 along their circumference 436. The membrane and thebackplate 430 may comprise a circular like or a square like form.Alternatively, the membrane and the backplate 430 may comprise anygeometrical suitable form.

The membrane and the backplate 430 may be connected to the substrate 410via an anchor region. The substrate 410 may further include activecomponents such as transistors, diodes, capacitors, amplifiers, filtersor other electrical devices. The substrate 410 may include an integratedcircuit (IC). The MEMS structure 400 may be a stand-alone device or maybe integrated with an IC into a single chip.

The membrane and/or the backplate 430 may comprise the conductivematerial layer and the dielectric layer as described with respect toFIG. 3 a.

The backplate 430 comprises large cutouts 420 and small cutout 425 alongthe circumference 436 of the backplate 430. The cutouts 420, 425 formanchor bridges 440 connecting the backplate 430 to the substrate 410(the anchor bridges 440 are part of the backplate 440). The cutouts 420,425 alternate with the anchor bridges 440. The cutouts 420, 425 maycomprise a parabola or a parabola like form. Alternatively, the cutouts420, 425 may comprise an oval, an oval like, a circular or a circularlike form. The anchor bridges 440 are grouped into groups of four.Alternatively, the anchor bridges 440 are grouped into groups of othernatural numbers. The cutouts 425 separate the individual anchor bridgesfrom each other within the group and the cutout 420 separate each groupfrom each other.

FIG. 4 b shows a single elongated protrusion 452 disposed on a singleanchor bridge 440. The elongated protrusion 452 comprises a length 1Rwhich is about the same as length 1A of the anchor bridge 440.Alternatively the length 1R of the elongated protrusion 452 is between ahalf and a full length of the length 1A of the anchor bridges 440. Inone embodiment, the elongated protrusion 452 overlies the rim region 415and the opening beneath the membrane and the backplate 430.

FIG. 4 c shows two elongated protrusions 452 per anchor bridge 440. Eachelongated protrusion 452 overlies anchor bridges 440, and a peripheralregion 437 of a central region 435 of the backplate 430. In oneembodiment the elongated protrusion 452 are disposed over the entirelength 1A of the anchor bridge 440. In other embodiments, the elongatedprotrusions 452 overlie the rim region 415 and the opening beneath themembrane and the backplate 430. The elongated protrusions 452 aredisposed along the circumference of the cutout 425 connectingneighboring anchor bridges 440. The elongated protrusions 452 in theanchor bridge 440 at the end of a group of four may or may not beextended to the next anchor bridge 440 of the next group of four.

The backplate 430 further comprises anti-sticking bumps 439 andanti-dampening openings 438. The anti-sticking bumps 439 may comprise acircular, a rectangular or a square region with a protruding portion.The protruding portion may be a middle tip or middle point. Theelongated protrusion 452 may be a stiffening ridge, a stiffening route,a stiffening track or a corrugation line. The elongated protrusion 452and the anti-sticking bumps 439 may be planar on the backside of thebackplate 430.

In one embodiment the anchor bridges 440 are about 5 μm to about 10 μmwide and about 100 μm long. The cutouts 425 may be about 10 μm to about20 μm wide, the backplate 430 may be about 1 μm to about 2 μm thick(e.g., about 1.64 μm thick), the elongated protrusion 452 width may be2× backplate 430 thickness (e.g., about 1 μm to about 3 μm) andelongated protrusion height may be about 1 μm to about 2 μm.

FIG. 5 a shows a top view of an embodiment of a MEMS structure 500. Thebackplate 530 and the membrane (not shown) are mechanically connected toa substrate 510 along their circumference 536. The membrane and/or thebackplate 530 may comprise a circular like, a square like form or a starlike form. Alternatively, the membrane and the backplate 530 maycomprise any geometrical suitable form.

The membrane and the backplate 530 may be connected to the substrate 510via an anchor region. The substrate 510 may further include activecomponents such as transistors, diodes, capacitors, amplifiers, filtersor other electrical devices. The substrate 510 may include an integratedcircuit (IC). The MEMS structure 500 may be a stand-alone device or maybe integrated with an IC into a single chip.

The membrane and/or the backplate 530 may comprise the conductivematerial layer and the dielectric layer as described with respect toFIG. 3 a.

The backplate 530 comprises large cutouts 520 and small cutouts 525along the circumference 536 of the backplate 530. The cutouts 520, 525form anchor bridges 540 connecting the backplate 530 to the substrate510 (the anchor bridges 540 are part of the backplate 530). The cutouts520, 525 alternate with the anchor bridges 540. The small cutouts 525may comprise a parabola or a parabola like form. Alternatively, thesmall cutouts 525 may comprise an oval, an oval like, a circular or acircular like form. The large cutouts 520 may comprise a rectangular orrectangular like form. Alternatively, the large cutouts 520 may comprisea parabola, a parabola like, an oval, an oval like, a circular or acircular like form.

The anchor bridges 540 are grouped into groups of two (2) and individualanchor bridges 540. Alternatively, the groups may comprise any othernatural number of anchor bridges 540 and the individual anchor bridges540 may comprise a plurality of anchor bridges 540. The cutouts 525separate the individual anchor bridges from each other within the groupand the cutout 520 separate the groups from the individual bridges 540.

FIG. 5 b shows two elongated protrusions 552 per anchor bridge 540. Eachelongated protrusion 552 overlies the anchor bridges 540, a peripheralregion 537 of a central region of the backplate 530. In one embodimentthe elongated protrusions 552 are disposed over the entire length 1A ofthe anchor bridge 540. In other embodiments, the elongated protrusions552 overlie the rim region 515 and the opening beneath the membrane andthe backplate 530. The elongated protrusions 552 are disposed along thecircumference of the cutouts 520, 525 connecting neighboring anchorbridges 540.

The backplate 530 further comprises anti-sticking bumps 539 andanti-dampening openings 538. The anti-sticking bumps 539 may comprise acircular, a rectangular or a square region with a protruding portion.The protruding portion may be a middle tip or middle point. Theelongated protrusions 552 may be a stiffening ridge, a stiffening line,a stiffening route, stiffening track or a corrugation line. Theelongated protrusions 552 and the anti-sticking bumps 539 may be planaron the backside of the backplate 530. The dimensions of the elongatedprotrusions, cutouts and the anchor bridges may comprise the samedimensions as before except for the large cutout which is between about20 μm to about 60 μm wide.

FIG. 6 a shows a top view of an embodiment of a MEMS structure 600. Thebackplate 630 and the membrane (not shown) are mechanically connected toa substrate 610 along their circumference 636. The membrane and/or thebackplate 630 may comprise a circular like, a square like form or a starlike form. Alternatively, the membrane and the backplate 630 maycomprise any geometrical suitable form.

The membrane and the backplate 630 may be connected to the substrate 610via an anchor region. The substrate 610 may further include activecomponents such as transistors, diodes, capacitors, amplifiers, filtersor other electrical devices. The substrate 610 may include an integratedcircuit (IC). The MEMS structure 600 may be a stand-alone device or maybe integrated with an IC into a single chip.

The backplate 630 and/or the membrane may comprise the conductivematerial layer and the dielectric layer as described with respect toFIG. 3 a.

The backplate 630 comprises large cutouts 620 and small cutout 425 alongthe circumference 636 of the backplate 630. The cutouts 620, 625 formanchor bridges 640 connecting the backplate 630 to the substrate 610(the anchor bridges 640 are part of the backplate 640). The cutouts 620,625 alternate with the anchor bridges 640. The cutouts 620, 625 maycomprise a rectangular or a rectangular like and/or parabola or aparabola like form. Alternatively, the cutouts 620, 625 may comprise anoval, an oval like, a circular or a circular like form. The anchorbridges 640 are grouped into groups of four (4). Alternatively, theanchor bridges 640 are grouped into group of other natural numbers. Thecutouts 625 separate the individual anchor bridges from each otherwithin the group and the cutout 620 separate each group from each other.In various embodiments the cutouts 620, 625 may comprise the samedimensions.

FIG. 6 b shows two elongated protrusions 652 per anchor bridge 640. Eachelongated protrusion 652 overlies anchor bridges 640, a peripheralregion 637 of a central region of the backplate 630. In one embodimentthe elongated protrusions 652 are disposed over the entire length 1A ofthe anchor bridge 640. In other embodiments, the elongated protrusions652 overlie a portion of the anchor bridge 640 such as the rim region615 and a portion of the opening beneath the membrane and the backplate630. The elongated protrusions 652 are disposed along the circumferenceof the cutout 625 connecting neighboring anchor bridges 640. Theelongated protrusions 652 in the anchor bridge 640 at the end of a groupof four may or may not be extended to the next anchor bridge 640 of thenext group of four.

FIG. 6 c shows two elongated protrusions 652 per anchor bridge 640. Eachelongated protrusions 652 overlies anchor bridges 640, a peripheralregion 637 of a central region of the backplate 630. In one embodimentthe elongated protrusions 652 are disposed over the entire length 1A ofthe anchor bridge 640. In other embodiments, the elongated protrusions652 overlie only a portion of the anchor bridge 640 such as the rimregion 615 and a portion of the opening beneath the membrane and thebackplate 630. The elongated protrusions 652 are disposed along thecircumference of the cutout 620 connecting neighboring anchor bridges640.

FIGS. 6 b-6 d show the elongated protrusions 653-655 extended towardsthe center of the backplate 630. For example, the elongated protrusions654, 655 of FIG. 6 c extend from the anchor bridge 640 to the center 660of the backplate 630 as shown in FIG. 6 d and the elongated protrusions653 of FIG. 6 b extends from the center of the cutout 620 to the center660 of the backplate 630. In one embodiment, only double elongatedprotrusions 654, 655 such as shown in FIG. 6 c cross the center 660 ofthe backplate 630. In an alternative embodiment only single elongatedprotrusions 653 such as shown in FIG. 6 d cross the center 660 of thebackplate 630.

In various embodiments the elongated protrusions on the anchor bridge652 which do not connect neighboring anchor bridges 640 extend towardsthe center of the backplate. In other embodiments various configurationsof elongated protrusions 652-655 may cross the center 660 of thebackplate 630.

The backplate 630 further comprises anti-sticking bumps 639 andanti-dampening openings 638 as shown in FIG. 6 d, for example. Theanti-sticking bumps 639 may comprise a circular, a rectangular or asquare region with a protruding portion. The protruding portion may be amiddle tip or middle point. The elongated protrusions 652-655 maycomprise stiffening ridges, stiffening lines, stiffening routes,stiffening tracks or corrugation lines. The elongated protrusions652-655 and the anti-sticking bumps 639 may be planar on the backside ofthe backplate 630. The dimensions of the elongated protrusions, cutoutsand the anchor bridges may comprise the same dimensions as described inprevious embodiment except for the large cutout which is between about20 μm to about 60 μm wide.

FIG. 7 shows an embodiment of a method 700 to manufacture a MEMSstructure. In step 710 a sacrificial layer is formed on a substrate. Thesubstrate may comprise a bulk mono-crystalline silicon substrate (or alayer grown thereon or otherwise formed therein), a layer of {110}silicon, a layer of {100} silicon, a silicon-on-insulator (SOI), or agermanium-on-insulator (GeOI). In various embodiments, the substrate mayinclude a blanket epitaxial layer. The substrate may comprise a compoundsemiconductor substrate such as indium antimonide, indium arsenide,indium phosphide, gallium nitride, gallium arsenide, gallium antimonide,lead telluride, silicon germanium, silicon carbide or combinationsthereof or glass.

The sacrificially layer comprises a dielectric material. For example,the sacrificial layer may be an oxide such as a silicon oxide, a nitridesuch as a silicon nitride, another isolating material or combinationsthereof. In one particular example, the sacrificial layer is tetraethylorthosilicate (TEOS).

In step 720 openings/recesses are formed in the sacrificial layer. Therecesses may comprise first type of recess (e.g., small recesses such asanti-sticking bumps) and a second type of recess (e.g., larger recessessuch stiffening ridges). In an optional embodiment the recesses mayfurther comprise a third type of recess (e.g., largest recesses such ascorrugation lines). The recesses may comprise the same depth. Forexample, the depth of the recesses may be 300 nm to 3000 nm.Alternatively, the depths of the recesses are different for each type ofopening. The first type of recess may be circular, oval or rectangularholes. The second type of recesses may comprise trench lines. The firsttype of recess comprises a width of about 300 nm to about 1500 nm andthe second type of recess comprises a width of about 1500 nm to about3000 nm. The width of the second type of recess may be chosen such thatthe top surface of the backplate is substantially planar.

The recesses are formed in the sacrificial layer with a directionaletch. A dry etch process or a wet etch process is applied. In oneparticular example, the openings are etched with an RIE. The recess maybe lined with a further sacrificial layer of conformal coating togenerate round corners at the upper edge of the opening.

In the optional step 730 the recesses are lined with a dielectric layer.The dielectric layer may comprise dielectric material such as siliconnitride, silicon oxynitride, silicon oxide or a polymeric. Thedielectric layer may be configured to provide tensile stress. Thedielectric layer may conformal overlie the bottom surfaces and thesidewalls of the recesses and the top surface of the sacrificial layer.The dielectric layer does not fill the recesses completely.

In step 740, a conductive layer is formed over the dielectric layer(otherwise over the sacrificial layer). The conductive layer may besilicon layer such as polysilicon, in-situ doped polysilicon orotherwise doped or undoped semiconductive layer. Alternatively, theconductive layer may be a metal layer. The conductive layer may comprisea plurality of layers. The conductive layer and the optional dielectriclayer form a backplate. In one embodiment the formation of thedielectric layer and the conductive layer is repeated to form a layerstack.

The conductive layer fills the opening and overlies the dielectriclayer. The conductive layer may be substantially planar over the smallopenings and the midsize openings. The conductive layer may form arecess over the backside of the large size openings.

In one embodiment the conductive layer comprises a thickness of about1000 nm to about 2000 nm and the dielectric layer comprises a thicknessof about 100 nm to about 200 nm. The thickness of the conductive layeris about 10 times larger than the thickness of the dielectric layer. Ina particular embodiment, the thickness of the conductive layer is about1600 nm and the thickness of the dielectric layer is about 140 nm. Thetop surface of the backplate is substantially planar for the first andthe second type of recesses. The height of the second type of recessesdepends on the depth etched into the sacrificial layer formed in step720 and is about 0.5 μm to about 2 μm.

In step 750 the substrate is removed underneath the backplate. Thesubstrate may be removed applying a Bosch™ etch process. The Bosch™ etchprocess may comprise repeating the following steps: 1) isotropic etchingsuch as a dry etching the substrate (wafer), 2) depositing a polymericfilm over the substrate (wafer) and the bottom surface and the sidewallsof the trench formed by the first etch step, and 3) opening thepolymeric film over the substrate (wafer) and the bottom surface of thetrench but not along the sidewalls so that step 1) can again be applied.

In step 760 the backplate (conductive layer and the optional dielectriclayer) is perforated with a directional etch. The sacrificial layer isthe etch stop layer.

In step 770, the sacrificial layer is removed underneath the backplate.Anti-sticking bumps may be formed from the first type of recesses andthe elongated protrusions may be formed form the second type ofrecesses. An isotropic etch process may be applied to remove thesacrificial layer through the perforation in the backplate. The membraneis released by removing the sacrificial layer. The anchor regions can beformed by controlling the timing of the isotropic etching or byproviding a covering such as a photo resist or passivation nitrideacross the anchor region avoiding the undercutting at this position.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method of forming a MEMS device, the method comprising: providing a substrate; and forming a backplate supported by the substrate, wherein the backplate comprises elongated protrusions, wherein forming the backplate comprises forming a center region, and forming anchor bridges connected to the substrate, and wherein the elongated protrusions are disposed on the anchor bridges.
 2. The method according to claim 1, wherein each anchor bridge comprises a radial elongated protrusion.
 3. The method according to claim 1, wherein two neighboring anchor bridges comprise a continuous elongated protrusion.
 4. The method according to claim 1, wherein each anchor bridge comprises a short elongated protrusion, the short elongated protrusion being disposed only on the anchor bridge, and a long elongated protrusion, the long elongated protrusion being connected to a neighboring anchor bridge.
 5. The method according to claim 1, wherein the elongated protrusions are disposed on areas of the backplate with maximum stress concentration.
 6. The method according to claim 1, wherein providing the substrate comprises providing a rim, and wherein the elongated protrusions overlie a portion of the rim.
 7. A method of forming a MEMS device, the method comprising: providing a substrate; and forming a backplate supported by the substrate, wherein the backplate comprises elongated protrusions, wherein forming the backplate further comprises forming anti-sticking bumps.
 8. The method according to claim 1, wherein the MEMS device is a microphone.
 9. A method of forming MEMS structure comprising: forming a movable electrode supported by a substrate; and forming a counter electrode supported by the substrate, wherein the counter electrode comprises elongated protrusions, wherein the method includes one or more of the following: wherein forming the counter electrode further comprises forming anti-sticking bumps, wherein forming the counter electrode comprises forming a plurality of anchor bridges connecting the counter electrode to the substrate, and wherein the elongated protrusions are disposed in the anchor bridges, wherein forming the counter electrode comprises forming a plurality of anchor bridges connecting the counter electrode to the substrate, and wherein each elongated protrusion connects neighboring anchor bridges, wherein forming the counter electrode comprises forming a plurality of anchor bridges connecting the counter electrode to the substrate, and wherein at least one of the elongated protrusions connect an opposite anchor bridge, and wherein the elongated protrusions are disposed in a center portion of the counter electrode.
 10. The method according to claim 9, wherein forming the counter electrode further comprises forming anti-sticking bumps.
 11. The method according to claim 9, wherein forming the counter electrode comprises forming a plurality of anchor bridges connecting the counter electrode to the substrate.
 12. The method according to claim 11, wherein the elongated protrusions are disposed in the anchor bridges.
 13. The method according to claim 9, wherein each elongated protrusion connects neighboring anchor bridges.
 14. The method according to claim 9, wherein at least one of the elongated protrusions connect an opposite anchor bridge.
 15. The method according to claim 9, wherein the elongated protrusions are disposed in a center portion of the counter electrode.
 16. The method according to claim 9, wherein forming the movable electrode comprises forming a membrane of a silicon microphone and forming the counter electrode comprises forming a backplate of the silicon microphone.
 17. The method according to claim 9, wherein the MEMS structure is a microphone.
 18. A method for manufacturing a MEMS structure, the method comprising: forming a sacrificial layer over a substrate; forming recesses in the sacrificial layer, the recesses comprising a first type of recess and a second type of recess, the first type of recess being different than the second type of recess; filling the first and second types of recesses with a conductive material; removing a portion of the substrate underneath the conductive material; and removing the sacrificial layer.
 19. The method according to claim 18, wherein the first type of recess comprises round holes and wherein the second type of recess comprises trenches.
 20. The method according to claim 18, wherein forming recesses further comprises forming a third type of recess, the third type of recess being different than the first type of recess and the second type of recess.
 21. The method according to claim 18, further comprising removing the sacrificial layer comprises releasing a membrane.
 22. The method according to claim 18, further comprising perforating the conductive material and removing the sacrificial layer through perforation holes. 